In future mobile communication system, for example, Beyond Third Generation (B3G) system or in LTE-A (Long Term Evolution Advanced) system, the system will provide higher peak data rate and cell throughput, and need larger bandwidth at the same time.
At present, unallocated bandwidth with frequency less than 2 GHz has been very little, and the partial or the whole bandwidth required by B3 G can only be found in the higher frequency band (such as the frequency band with frequency higher than 3 GHz). In actual application, the higher the frequency band is, the faster the radio wave propagation attenuation will be and the shorter the transmission distance will be. Therefore, in the same coverage area, more base stations are needed to ensure the continuous coverage. However, since the cost of base station is high, this will undoubtedly increase the cost of network layout. In order to solve the problems concerning network layout cost and coverage, various manufacturers and standard organizations begin the research on introducing relay node (RN) into cellular system so as to increase network coverage.
FIG. 1 is the diagram of the network architecture of existing LTE-A system after RN is introduced therein. RN accesses core network through donor cell under the DeNB (Donor evolved Node B), but there is no direct wired interface between RN and core network. Each RN can control one or more cells. Under such architecture, the interface between UE (User Equipment) and RN is Uu interface, while that between RN and DeNB is Un interface.
Backhaul link refers to the link between access network and core network. Un interface is a part of the backhaul link, and is a kind of wireless backhaul link. In order to avoid interference, DeNB and RN shall discuss with RN on which sub-frames data shall be sent and received. For example, when DeNB sends downlink data to RN on some sub-frames, RN cannot send downlink data to UE on the same sub-frames, or it will cause inner equipment co-frequency interference of RN. When it is determined that sub-frame shall be divided between DeNB and RN, DeNB shall be responsible for completing sub-frame configuration and sending the allocated backhaul sub-frame configuration information to RN through RN reconfiguration process.
Establishing process of X2 is used for configuration data of application layer on interactive X2 interface between the two eNBs to make the two eNBs intercommunicate normally through X2 interface. When establishing the X2 interface, the configuration data of interactive application layer required between the two sides include ECGI (E-UTRAN Cell Global Identifier, evolved universal terrestrial radio access network cell global identifier) of the cell, PCI (Physical Cell Identifier), downlink frequency, etc. FIG. 2 shows the flow diagram of X2 interface establishing process in the prior art.
Similarly, in FIG. 1, X2 interface is established between eNB (evolved Node B) and DeNB, and between DeNB and RN, thus realizing the communication between base stations (DeNB has eNB property itself, while with respect to the self-service terminal equipment, RN also has the functions of eNB).
When the application layer configuration data of X2 interface of eNB change, eNB will notify adjacent eNB through eNB configuration and update process to make the two eNBs operate normally on X2 interface. Wherein, the application layer configuration data that may be updated include ECGI, PCI, downlink frequency, etc. FIG. 3 is the flow diagram of eNB configuration update process in the prior art.
X2 handover includes three stages: handover preparation, handover execution and route switch (also referred to as handover completion), as shown in FIG. 4, which is the flow diagram of X2 handover process in the prior art Handover preparation is initiated by source eNB to determine which target eNB shall be handed over to. Handover command message generated by carrying target eNB in handover request acknowledgement message is sent to UE by source eNB.
In the application scene with RN, after receiving handover request message, DeNB reads the target cell identifier therein, and then forwards the handover request to corresponding target base station.
In the prior art, when selecting donor cell, RN will select a proper cell to access according to the frequency of Uu interface itself and that of donor cell, and judge if DeNB is required for allocating special sub-frames used on backhaul for itself. Then RN will notify the judgment result to DeNB in RRC (Radio Resource Control) message.
In the process of realizing the present invention, at least the following problems are found in the prior art by the inventor:
When handover occurs due to RN moving, the donor cell accessed by RN changes, and the frequency used by target donor may be different from that used by original donor cell. Therefore, working state of RN may change. For example, “resource partitioning is required” mode is changed to “resource partitioning is not required” mode, or vice versa. However, how to configure backhaul sub-frame information is not described in the prior art under the condition that the attributive donor cell of RN is changed.